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Gut microbes

RYGB dramatically alters gut microbes compared to LAGB

The resulting post-surgical composition of gut microbes observed for RYGB patients was distinct from both normal weight and obese patients, and displayed the high microbial diversity associated with a healthy gut

A study comparing Roux-en-Y gastric bypass (RYGB) and laparoscopic adjustable gastric banding (LAGB) has reported that bypass produces profound changes in the composition of microbial communities in the gut, with the resulting gut flora distinct from both obese and normal weight patients. The results are likely due to the dramatic re-organisation of the gut caused by RYGB surgery, which increases microbial diversity. The research could highlight new diagnostics and therapies for obesity.

In the study, ‘Distinctive microbiomes and metabolites linked with weight loss after gastric bypass, but not gastric banding ’, published in the  journal International Society for Microbial Ecology (ISME), Drs Zehra Esra Ilhan and Rosa Krajmalnik Brown, and their colleagues at the Biodesign Institute at Arizona State University (ASU), along with researchers from Mayo Clinic, and Pacific Northwest National Laboratory, explored microbial communities in the human gut following RYBG and LAGB surgeries.

“Another positive outcome would be if we can find a microbial biomarker that will identify the best candidates for surgery and sustained weight loss."

"This is one of the first studies to show that anatomically different surgeries with different success rates have different microbiome and microbiome-related outcomes," said Ilhan, lead author of the new paper. The results also indicate that correction of obesity tends to improve related metabolic conditions, including diabetes and high cholesterol.

The results confirmed their earlier research with a smaller sample size, showing that in the case of the more aggressive RYGB surgery, microbial communities underwent a profound and permanent shift following weight loss. The resulting post-surgical composition of gut microbes observed for RYGB patients was distinct from both normal weight and obese patients, and displayed the high microbial diversity associated with a healthy gut.

The current study also applied the technique of nuclear magnetic resonance (NMR) to examine the metabolome, a composite of the metabolites produced by the various microbes in the gut. The outcomes showed significant alterations as a result of the RYGB procedure. In the case of the alternate treatment, LAGB, changes in the gut microbiota were mild and accompanying weight loss was less pronounced.

The four images indicate the degree of microbial diversity in the gut in normal patients as well as in obese patients before and after undergoing two types of weight-loss surgery. The normal human gut has a high degree of microbial diversity, considered important for the maintenance of health. Obese patients have lost much of this diversity and while laparascopic band surgery effectively leads to weight loss, the low microbial diversity condition remains. By contrast, gastric bypass surgery results in the restoration of microbial diversity in the gut, though the composition of microbes is distinct from both normal weight and obese patients (Credit: Jason Drees for the Biodesign Institute)

"One of the key findings of the paper confirms what we had already observed in earlier research. RYGP gastric bypass had a huge effect on the microbial community structure," said Krajmalnik Brown. This fact may have profound implications for both the understanding and management of obesity.

The millions of bacterial microbes in the human gut perform a vast range of critical functions in the body and have even been implicated in mood and behavior. Among their critical responsibilities are the micro-management of nutrients in the food we digest, hence their central place in the regulation of body weight.

Krajmalnik-Brown explained that diversity of gut microbes is essential to good health.  Low microbial diversity in the gut is associated not only with obesity but a range of ailments including inflammatory bowel disease, ulcerative colitis and autism.

The study sought to explore long-term changes in the gut in patients who had undergone either of the two surgeries at least nine months prior, comparing them with normal weight and pre-bariatric obese patients. While the reasons for the sharp disparity of results between RYGB and gastric banding are not entirely clear, the results indicate that simply reducing the size of the stomach through gastric banding is not sufficient to induce the large changes in microbial communities observed for the RYGB group.

One hypothesis the authors put forward is that RYGB alters the physiology of the gut to such a degree that microbes formerly unable to survive conditions in the obese gut are able to flourish in their surgically-modified surroundings.

"One of the things we observe from the literature is that the oral microbiome community composition is very similar to the colon microbiome composition after bariatric surgery," said Ilhan. "You're giving new microbes a chance to make it. Most of the species are acid sensitive, which supports the idea that changes in stomach pH levels may permit these microbes to survive and make it to the colon."

While it seems clear that RYGB surgery produced permanent changes in bacterial communities in the gut, the resulting microbial community may also act to help maintain weight loss over the long term. Experiments have shown that transplantation of beneficial microbes from mice that have undergone RYGB surgery into obese mice induces dramatic weight loss. While these results have yet to be replicated in humans, the findings open the door to the eventual use of healthy microbial communities to treat obesity.

"These new data on microbial community structure and function significantly expand our knowledge on how the microbiome is associated with weight loss following bariatric surgery,” said Dr John DiBaise, a gastroenterologist at Mayo Clinic, Scottsdale and co-author of the new study.

Although the RYGB surgery has been quite successful for many patients suffering from morbid obesity, for some patients surgery is not successful and they regain the weight they have lost post-surgery, perhaps because they lack the favourable microbes necessary for permanent weight loss.

"A probiotic that would replace surgery would be great,” concluded Ilhan. “Another positive outcome would be if we can find a microbial biomarker that will identify the best candidates for surgery and sustained weight loss."

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